Most investigations on the nature of vascular dysfunction in hemorrhagic shock have implied changes in microcirculatory behavior. A few studies have yielded direct qualitative observations of microcirculatory behavior but these required general anesthesia and exteriorized tissues. Recent work has indicated that the bat (Myotis lucifugus) can be used as an adequate shock model for investigating the changes in microcirculatory activity in a system which is uncomplicated by major surgery or anesthesia. This project provides a direct quantitative investigation of the responses of small veins, postcapillary venules and their associated arteries and arterioles to hemorrhagic hypotension. These responses will be quantitated for subcutaneous microvasculature in the wings of unanesthetized bats (Myotis lucifugus) and for skeletal muscle microvasculature in the cremaster of rats anesthetized with urethane-chloralose or pentobarbital when these animals are exposed to reversible and irreversible hemorrhagic shock states. Data is acquired with closed-circuit television methods and reduced through digital computer techniques. In general, our current hypothesis focuses on the venules as a microcirculatory segment which is critically altered during hemorrhagic shock. At the present time, studies on the effect of anesthesia, hypoxia, hypercarbia, and pharmacological blockade on small arteries (35-45 microns) and veins (70-100 microns) have been completed for the bat wing and are underway for the rat cremaster preparation.